Low-carbohydrate diets such as the keto diet and the Atkins diet have gained popularity as a quick way to lose weight. But is this short-term gain worth the long-term consequences? Recently the results of two studies have been released that stack up more data against eating the low-carb way. These are both very large prospective epidemiological studies that looked at the effect that food choices have on living a long, healthy life. The first one was published in the Lancet on September 1, 2018 (1) and the second was released at the European Society of Cardiology Congress 2018 (2). Both studies reached the same conclusion – that risk of early death increases as intake of carbohydrates decrease.
The Lancet Study: Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis (1)
This investigation is part of the Atherosclerosis Risk in Communities (ARIC) study which is an ongoing, prospective observational study of cardiovascular risk factors in four diverse US communities (Forsyth County, NC; Jackson, MS; suburbs of Minneapolis, MN; and Washington County, MD). In this study, 15,428 adults whose dietary energy intake was not either extremely high or extremely low (within 600 kcal and 4200 kcal per day for men and within 500 kcal and 3600 kcal per day for women) completed a dietary questionnaire between 1987 and 1989 and then they were followed for over 25 years. Participant information was updated five times over the course of the study. These interim visits occurred between 1990 and 1992, between 1993 and 1995, between 1996 and 1998, between 2011 and 2013 and between 2016 and 2017. The primary focus of the study was the effect of eating carbohydrates on all-cause mortality. Researchers also looked at the source of the food that was used to replace carbohydrates and the differing changes in mortality rates that occurred depending on whether the carbohydrates were replaced by animal sources of fat and protein or plant sources of fat and protein.
Results of the study showed a U-shaped association between the percentage of energy consumed from carbohydrate sources and early death. In other words, when looking at total carbohydrate intake without regard to where those carbohydrates came from, a diet containing 50 to 55% of energy from carbohydrate was associated with the lowest mortality risk while low carbohydrate consumption (less than 40%) or high carbohydrate consumption (greater than 70%) showed greater risk of early death from all causes. Note that diets with very high carbohydrate levels often reflect poor food quality with greater reliance on refined carbohydrates such as white sugar, white flour and white rice (3).
Interestingly these results varied according to the source of the foods chosen to replace the carbohydrates. If the replacement for carbohydrate was derived from animal protein or fat the risk for early mortality was significantly larger. Conversely, mortality was reduced by about the same amount when carbohydrate was replaced with plant-derived protein or fat.
Researchers carefully examined the sources of the protein and fat that were used to replace carbohydrates in the diet and here is what they found.
A more plant-based low-carbohydrate diet was associated with higher average intake of vegetables and lower average fruit intake.
A more animal-based low-carbohydrate diet was associated with lower average intake of both fruit and vegetables.
All low-carbohydrate diets increased intake of fat in exchange for carbohydrates but choosing plant-based replacements resulted in a diet higher in polyunsaturated fat and lower in saturated fat compared to the animal-based choice.
Total protein intake was also higher in the animal-based diet compared to the plant-based one.
Choosing animal-based foods to replace carbohydrates translated into more daily servings of beef, pork, lamb, chicken and cheese.
Choosing plant-based foods to replace carbohydrates translated into more daily servings of vegetables, nuts, peanut butter, chocolate, white breads and whole-grain breads.
Increased consumption of animal-based protein and fat instead of carbohydrate was associated with a significant increase in all-cause mortality.
Increased consumption of plant-based protein and fat instead of carbohydrate was associated with a significant decrease in all-cause mortality.
The European Society of Cardiology Congress report: Low Carbohydrate diets are unsafe and should be avoided (2)
This is another prospective study that looked at the relationship between low-carbohydrate diets and death from all causes as well as deaths specifically from coronary heart disease, cerebrovascular disease (including stroke) and cancer. The study gathered 24,825 participants from the NHANES survey (US National Health and Nutrition Examination Survey) and followed them from 1999 to 2010. Results showed that as carbohydrate intake fell the risks of both all-cause and cause-specific death increased. Those with the lowest intake of carbohydrates had a 32% higher risk of early death from all causes compared to those eating the highest amount of carbohydrates. Moreover risks of death from coronary heart disease were increased by 51%, risks of cerebrovascular-related death were increased by 50% and risks of cancer-related death were increased by 35% in those eating the lowest amount of carbohydrates compared to those eating the most. These results remained significant after adjusting for all other factors that might have influenced the associations.
Researchers looked more deeply into effects of a low-carbohydrate diet on the obese (BMI 30 or greater) as compared to the non-obese (BMI under 30) and found that the link was strongest in the non-obese participants.
These results were validated in an accompanying meta-analysis of seven previous prospective cohort studies that included 447,506 participants followed up for 15.6 years. Over all seven studies increased risks of death were associated with low-carbohydrate diets, specifically 15% increased early death from all causes, 13% increased risk of early death from cardiovascular causes and 8% increased risk of early death from cancer.
What are these two trials telling us?
The health that we enjoy is dependent on eating more healthy nutrients and less detrimental ones. Choosing a low-carbohydrate diet inevitably means eating more protein and fat along with fewer fruits and vegetables when compared to a diet higher in carbohydrates. Low-carbohydrate diets of any kind followed over a long period of time incite inflammation and oxidative stress (4,5,6,7,8). Beyond that, choosing a low-carbohydrate diet high in animal-based foods results in eating much higher amounts of health-damaging nutrients such as animal protein, saturated fat, cholesterol and heme iron (9,10,11,12). High amounts of animal-based foods unavoidably crowd out plant-based foods thereby limiting beneficial nutrients such as fiber, phytochemicals, vitamins, minerals, unsaturated fatty acids and n-3 fatty acids. Though the plant-based choices were not itemized in the Lancet study, researchers noted that participants choosing plant-based fats and proteins as replacements for carbohydrates consumed more vegetables, nuts, peanut butter, chocolate and whole-grain breads than those choosing animal-based replacements.
Diets high in fiber and whole carbohydrates such as fruits, vegetables, whole grains, nuts, seeds and legumes, while low in fats, refined grains and red and processed meats have been repeatedly associated with lower risks of coronary heart disease, stroke and other chronic diseases (13,14,15,16). Research in the Blue Zones of the world, areas around the world where the longest-living people reside, reveals that these people eat a predominantly whole-food, plant-based diet high in whole grains, legumes, nuts, fruits and leafy vegetables. Their diets often provide more than 65% of daily calories from carbohydrates. Note however that the carbohydrates eaten by people in the Blue Zones are whole foods, not the refined and processed carbohydrates found in foods such as white bread and high-sugar beverages (17).
Because these two studies are observational and prospective in nature they cannot prove cause and effect. But they do serve to strengthen the evidence we already have about the unhealthy nature of long-term low-carbohydrate diets compared to more nutritious diets that emphasize high amounts of whole carbohydrate-containing foods (18,19,20,21,22).
Concluding statements from these two trials succinctly sum up their results.
Author Maciej Banach of the Medical University of Lodz, Poland says of the European Society of Cardiology Congress report, “The findings suggest that low carbohydrate diets are unsafe and should not be recommended.”
The conclusion of the Lancet study states, “These data also provide further evidence that animal-based low-carbohydrate diets should be discouraged.”
Finally, if a choice has been made to restrict carbohydrates for goals such as weight loss, replacing carbohydrates with plant-based fats and proteins is the healthiest path to follow.
1 Seidelmann, S.B., Claggett, B., Cheng, S., Henglin, M., Shah, A., Steffen et al. Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis. Lancet Sept 1, 2018; 3(9):PE419-E428.
2 Banach, M. Low Carbohydrate diets are unsafe and should be avoided. August 28, 2018; European Society of Cardiology Congress 2018. https://www.eurekalert.org/pub_releases/2018-08/esoc-lcd082318.php
3 Nakamura, Y., Okuda, N., Okamura, T. et al. Low-carbohydrate diets and cardiovascular and total mortality in Japanese: a 29-year follow-up of NIPPON DATA80. Br J Nutr. 2014; 112: 916-924.
4 O’Keefe, H., Gheewala, N.M., O’Keefe, J.O. Dietary Strategies for Improving Post-Prandial Glucose, Lipids, Inflammation, and Cardiovascular Health. J Amer Coll Cardiology Jan 2008; 51(3): 249-255.
5 Vitale, M., Masulli, M., Rivellese, A.A., Babini, A.C., Boemi, M., Bonora, E., Buzzetti, R., Ciano, O., Cignarelli, M., et al. Influence of dietary fat and carbohydrates proportions on plasma lipids, glucose control and low-grade inflammation in patients with type 2 diabetes—The TOSCA.IT Stud. European Journal of Nutrition June 2016; 55(4):1645-1651.
6 Fitó, M., Guxens, M., Corella, D. et al. Effect of a traditional Mediterranean diet on lipoprotein oxidation. Arch Internal Med, 167 (2007): 1195-1203.
7 Mitrou, P.N., Kipnis, V., Thiebaut, A.C. et al. Mediterranean dietary pattern and prediction of all-cause mortality in a US population: results from the NIH-AARP Diet and Health Study. Arch Intern Med, 167 (2007): 2461-2468.
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12 Hu, F.B. Plant-based foods and prevention of cardiovascular disease: an overview. Am J Clin Nutr. 2003; 78: 544S-551S
13 Fung, T.T., Willett, W.C., Stampfer, M.J., Manson, J.E., Hu, F.B. Dietary patterns and the risk of coronary heart disease in women. Arch Intern Med. 2001 Aug 13-27; 161(15):1857-1862.
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15 Song, M., Fung, T.T., Hu, F.B., et al. Association of animal and plant protein intake with all-cause and cause-specific mortality. JAMA Intern Med 2016; 176: 1453–1463.
16 Hu, F.B. Plant-based foods and prevention of cardiovascular disease: an overview. Am J Clin Nutr. 2003 Sep; 78(3 Suppl):544S-551S.
17 Buettner, Dan (2012). The Blue Zones, Second Edition: 9 Lessons for Living Longer From the People Who’ve Lived the Longest. Washington, D.C.: National Geographic. ISBN 978-1426209482. OCLC 777659970.
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